Journal of Chemical Engineering of Japan, an official publication of the Society of Chemical Engineers, Japan, is dedicated to providing timely original research results in the broad field of chemical engineering ranging from fundamental principles to practical applications. Subject areas of this journal are listed below. Research works presented in the journal are considered to have significant and lasting value in chemical engineering.

Conventionally, both aeration tanks and bubble columns are supplied oxygen from dispersed bubbles. However, the geometry of the aeration tanks is greatly different from that of bubble columns. Although almost all oxygen is absorbed from dispersed bubbles in the water for bubble columns, the aeration tank has such a large free surface area that the oxygen transfer from atmosphere cannot be neglected. Therefore, it is very important to investigate oxygen transfer from not only the free surface, but also bubbles. In this study, the volumetric oxygen transfer coefficient, gas holdup and its two dimensional profile were measured in a large scaled aeration tank of typical size for industrial sewage treatment. Moreover, the effect of the aeration method on gas holdup and water circulation such as spiral flow aeration and whole floor aeration were also investigated. By analyzing the experimental results, a simultaneous oxygen transfer model which consists of the sum of oxygen transfer coefficients not only between bubbles and water, but also between the atmosphere and the free surface, is proposed. The model was evaluated by comparing with two alternative models for the experimental overall oxygen transfer coefficients. The proposed model estimated the experimental results better than the other models.

In a novel high-speed disperser, the dimension and flow characteristics of highly viscous liquid (syrup) filaments were investigated, in order to lay the foundation for further study of the mass transfer of polymer devolatilization in the high-speed disperser. Results showed that the mean syrup filament diameter decreased with the increase of rotational speed and radial distance. Meanwhile, the mean syrup filament radial velocity increased with increasing rotational speed, but the variation trend of the mean syrup filament radial velocity with increasing radial distance was divided into three stages: ascending, steady and descending stage. The mean syrup filament tangential velocity also increased with increasing rotational speed; nevertheless, it increased initially, but decreased rapidly afterwards as the radial distance increased. Based on the experimental data of syrup filament velocity, the syrup filament shape was successfully modeled to obtain the bending degree, length, and specific surface of unit volume of syrup filament. In the meanwhile, the mean residence time and the number of syrup filament at different rotational speeds in the entire cavity zone were calculated, then offering essential information to further realize high-efficiency polymer devolatilization in the current high-speed disperser.

The present study simulates gas–liquid flows in different scale pipes. Based on the Frank model, emphasis is placed on the acting distance of wall lubrication force from the wall. The acting distance is not constant; whereas, it is the function of device scale. After the modifications, the new model is employed to simulate the gas–liquid flow in a Transient Two-Phase Flow (i.e., TOPFLOW) and Multiphase Loop (i.e., MTLoop) apparatus, using the commercial software ANSYS Fluent. The cases with different superficial air velocities and different ratios of length to diameter were studied. The results indicated that calculated data for the radial gas holdup and radial bubble velocity magnitude were in good agreement with experimental data. The modified model can be used to predict the water–air flow at room temperature in bubble columns in which the coalescence and breakup of bubbles are not obvious.

The transmittance of slime water is one of the more important evaluation indexes for slime water treatment. This study analyzes the importance of cooperative treatment on the slime water by microbial and chemical reagents and tests of its basic properties. A model equation and theoretical analysis are provided through experimental work, model analysis and data processing. In addition, the micro effect mechanism of the cooperative treatment is explained. The experimental results demonstrated that the experimental slime water has a high content of fine mineral particles with particle size of less than 20 µm in 85% slime water. Particles with size of less than 5 µm take up half the content of the slime water. Since most coal slurries are SiO2, Al2O3 contained clay minerals, it is easy for them to form colloidal particles with strong negative charges. The content of slime ash in the slurry is very high, resulting in difficult settlement of mineral particles. Using the experimental data, a quadratic model equation is built employing the transmittance of the supernatant of slime water as response index. This equation points out the optimum quantity of the microbial reagent. In addition, it was found that both the microbial reagent and polymer flocculant interact with CaCl2 obviously. The theoretical analysis explains the micro separation mechanism for mineral particles and water-solid-liquid mixture. The addition of microbial reagent disrupts the charge balance of the slime water and CaCl2 increases the coagulation effect. The polymer flocculant produces highly effective flocculating settlement. The three reagents have a synergistic effect on slime water and achieve an ideal transmittance of 92%.

A simulation code based on the discrete element method (DEM) and computational fluid dynamics (CFD) coupling model was developed to simulate the behavior of radioactive cesium in waste incinerators. The waste lump was represented by particles in the simulation. The energy equation for a mixed gas, diffusion equation for each gas component, as well as the energy, drying, pyrolysis, and combustion equations for each particle were solved in the simulation by adding a combustion model to the standard DEM–CFD coupling model. The particle size of the waste changed as drying, pyrolysis, and combustion progressed. At the end of the combustion process, particle waste became ash, and the number of ash particles was enormous. To avoid an excessive computational load due to the high particle number, a similar assembly model was adopted to reduce the particle number in the calculation. There was a good agreement between the simulation and experimental results for the temperature at the outlet of the furnace and the flue gas composition.

The present study numerically and experimentally investigates the turbulent flow and heat transfer enhancement mechanisms of a serpentine air preheater, and further, the influence of geometrical parameters on thermal enhancement and flow resistance as well. The numerical simulation results coincided well with the experimental data. The results indicated that the structure with smaller path height ratios (HR=H/W) had promising enhancement capabilities, but larger pressure drop at the same time. Here, the factor HR is the ratio of height to width of the effective heat transfer flow path. The larger effective path length (Le) had a positive effect on the thermal-hydraulic performance at lower Re number (Re<2,200), while smaller Le displayed better performance on thermal enhancement at higher Re number (Re>2,200). With the nonlinear multiple regression methods, correlation for the averaged Nusselt number (Nu) was fitted by geometrical parameters Le, HR and Re number.

The leaching of cerussite kinetic was investigated using sulfamic acid solution as lixiviant. Results showed that 30 min was the optimum time to achieve over 95% lead extraction under the following leaching conditions: temperature of 60°C, stirring speed of 1,000 rpm, average particle size of 60 µm, and sulfamic acid concentration of 0.3 mol/L. The leaching process was controlled by the shrinking core model for surface chemical reaction. The leaching rate increased with increased reaction temperature, stirring speed, and concentration, as well as with decreased particle size. The apparent activation energy was 47.57 kJ/mol, and the reaction orders with respect to stirring speed, sulfamic acid concentration, and particle size were 1.683, 1.165, and −0.764, respectively. XRD and SEM analyses indicated that cerussite almost was completely dissolved and leaching residues included quartz. Therefore, sulfamic acid solution can be used as effective lixiviant for lead extraction from cerussite.

Mesoscale simulations of particle rejection by a microfiltration membrane during pressure-driven, dead-end filtration were carried out using a “SNAP” (Structure of NAnoParticles) simulator. We demonstrate that surface porosity and the ratio of particle to pore diameter (d/dm) strongly affect particle transport and rejection behaviors. Two subsequent fouling modes, characterized by differing fouling origins, are described and the fouling dynamics are discussed in detail. In the first case, fouling begins on the front of the membrane and the cake layer is formed when the surface porosity is low and when d/dm is high. In the second case, fouling begins on the back of the membrane and pore clogging evolves when the surface porosity is high and d/dm is low. We also demonstrate that flux profiles depend on the fouling mode.

In this study, the effect of the catalyst pretreatment temperature, which is one of the more important factors in HCHO oxidation at room temperature over Pd catalysts, was examined. To evaluate the effect of the pretreatment temperature on the catalytic activity, Pd-supported catalysts were prepared at temperatures ranging from 673 to 1,073 K under a hydrogen atmosphere. The correlation between the pretreatment temperature and catalytic activity produced a volcano-shaped plot. X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller analysis, and CO chemisorption confirmed that the catalytic activity highly depended on the Pd size or dispersion.

1-Allyl-pyridinium type ionic liquids with acidic anions were synthesized using a microwave-assisted method to develop a one-pot method for the direct saccharification of cellulose. A monosaccharide yield of ca. 52.4% was obtained by processing the cellulose at 100°C for 1 h using a novel ionic liquid (i.e., 1-allyl-pyridinium methanesulfonate) without an additional catalyst. The first principles molecular dynamics simulations and investigations of the electronic structures of ionic liquids and cellulose revealed the mechanism of the direct saccharification of cellulose. An anion with –SO3− attracts H+ dissociated from H2O, which causes the temporary formation of the –SO3H group. Next, the –SO3H functions as an acid catalyst to hydrolyze the cellulose. In saccharification, appropriate cations, such as the 1-allyl-pyridinium cation, also play important roles. The cation interacts with the cellulose to weaken the primary chain bonds of the cellulose, which enables the decomposition of cellulose.

Knowledge of the relationship between the activity and structural features of enzymes is critical for designing conjugation materials. Nonetheless, few studies have addressed the decrease in enzyme activity after modifications of the corresponding enzymes. In cytochrome P450cam, the structural changes around the heme active center can be easily evaluated by spectrophotometric analysis. Thus, with the use of P450cam, we evaluated the relationship between enzyme activity and structural changes after its modification. Our study revealed the existence of a new mode for P450 activity downregulation, which was distinct from a well-known inactivation mode for the conversion of P450 to the inactive P420 form. In this new mode, the activity decreased due to a reduction in binding or accessibility of a substrate to the heme pocket of P450cam, while the enzymatic tertiary structure was retained after conjugations.

The present study developed a microdevice for reduction of nitrate ion made of zinc or copper with the purpose of reducing the impact on the environment. The performance was evaluated by reduction of nitrate ion in a nitric acid aqueous solution of 10−2 mmol/L (10−2 mol/m3) as a sample. Nitrate ion was reduced to nitrite ion using a microdevice made of zinc, which is environmentally–friendly reductive reagent. The behavior at shorter contact time to zinc was considered to come from the adsorption process of nitrate ion to zinc before a reduction process. However, the reduction efficiency of nitrate ion remained 12.1% at 0.067 µL/s (6.7×10−11 m3/s), which corresponded to a longer contact time to zinc of 120.4 s. Moreover, bonding between the zinc and polydimethylsiloxane (PDMS) substrates did not last long. On the other hand, nitrate ion was reduced to nitrite ion using a microdevice made of copper, which was made by a fabrication method enabling seamless bonding. The reduction efficiency of nitrate ion reached 79.4% at 0.083 µL/s (8.3×10−11 m3/s) in the microdevice with the single-layered structure, and 62.0% at 0.25 µL/s (2.5×10−10 m3/s) in the microdevice with the four-layered structures. The microdevice made of copper showed about 6 times the reductive ability for nitrate ion compared with that made of zinc. Also, the flow rate range of nitric acid aqueous solution using the microdevice with the four-layered structure was larger. The microdevice with the four-layered structure having larger flow contributed to improving versatility. Furthermore, the internal volume in the microdevice was only 10.5 µL (1.05×10−8 m3), and thus the sample volume in the microdevice was obviously much smaller than that of 200 µL (2.0×10−7 m3) in the flow injection analysis (FIA) method. Therefore, using a microdevice might keep the impact of copper on the environment to a minimum.

Bimetallic Pt–Ru nanoparticles were successfully synthesized using a reducing bacterium, Shewanella algae (S. algae), by the bioreduction of Pt(IV) and Ru(III) in an aqueous solution, where H2PtCl6 and RuCl3 were dissolved. These bimetallic nanoparticles were expected to be preferably used as catalyst in a direct methanol fuel cell (DMFC) because inactivation of their catalytic activity can be avoided by the effect of Ru to remove CO from Pt surface. In this study, two patterns in mixing procedure of H2PtCl6 and RuCl3 were compared for the synthesis of the catalyst particles by the bioreduction. The open circuit voltage was monitored at a DMFC using the electrodes with catalyst nanoparticles synthesized by the bioreduction of S. algae. Continuous inactivation of the catalytic activity of the nanoparticles was observed when the nanoparticles were synthesized with continuous admixture of RuCl3 to H2PtCl6 during the bioreduction or without RuCl3. On the other hand, the inactivation was stopped to preserve the open-circuit voltage when H2PtCl6 and RuCl3 were mixed prior to the bioreduction. This feature which is preferable for DMFC can be ascribed to alloying Ru with Pt in the resulted nanoparticles. It is remarkable that Ru(III) which is hardly reduced by S. algae due to its relatively low standard electrode potential can be alloyed with Pt to produce the bimetallic Pt–Ru nanoparticles in the present condition.